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Carbohydrates

2.6

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CarbohydratesCarbohydrates are made from CARBON, HYDROGEN and OXYGEN

FUNCTION 2:Plant cell walls depend on the STRUCTURAL role of some carbohydrates

FUNCTION 1:They STORE ENERGY in plants and animals

MONOSACCHARIDES

CARBOHYDRATES

POLYSACCHARIDESDISACCHARIDES

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(CH2O)n

MonosaccharidesMonosaccharides are small organic molecules used as bulding blocks for more complex carbohydrates. Click each of the blue boxes to work through the slide.

General FormulaWhat does the ‘n’

stand for?

Number of Carbon atoms

So, when n=3TRIOSE, e.g. glyceraldehyde -

In metabolic reactions

When n=5 When n=6

HEXOSE, e.g. glucose -

main source of energy

PENTOSE, e.g. ribose –

formation of nucleic acidnextnext

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sMONOSACCHARIDES

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Monosaccharides can exist as straight chain and ring forms.

The ring forms are common when glucose is in solution.

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sIsomerism in Glucose C6H12O6

CHCH22OHOH

CHCH22OHOH

Alpha-glucose

beta-glucose

Show structural changeShow structural change

Oxygen

Hydrogen

Carbon

Hydroxide (OH)

Glucose forms two isomers

They both have the same molecular formula but a different structure

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s Both these molecules are glucose.

Both have a molecular formula of C6H12O6.

But they are structurally different.

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As an energy source…..

•A large amount of energy is stored between the C-H bonds•This is released to form ATP•ATP is the energy currency of the cell

As building blocks…..

•Repeated glucose molecules build up; starch & glycogen•Ribose (5C) forms part RNA•Deoxyribose (5C) forms part DNA

Biological role of monosaccharides

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GLUCOSE

MALTOSESUCROSE

GLUCOSE

GLUCOSE

Disaccharides

A disaccharide can be made from two of the same

monosaccharide molecule or from two different ones.

Disaccharides form when two monosaccharide units join forming a

glycosidic bond, by a condensation reaction.

The combination of monosaccharides determines which disaccharide is formed.

MONOSACCHARIDES DISACCHARIDE

FRUCTOSEGALACTOSE

WATERWATERWATER

LACTOSE

GLUCOSE

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Most common disaccharides

Monosaccharide Disaccharide Found in !

Glucose and glucose Maltose Malt sugar

Glucose and fructose Sucrose Cane sugar

Glucose and galactose

Lactose Milk sugar

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OOHOH

Forming Disaccharides

C C

C

C O

C

H

OH

OHOH

OH

HH

CH2OH

H

H

CHCH22OHOH

C C

C

C O

C

H

OH

OHOH

OH

HH

CH2OH

H

H

C C

C

C O

C

H

OH

OH

OH

HH

CH2OH

H

H

C C

C

C O

C

H

OH

OH

OH

HH

CH2OH

H

H O

H H

GlycosidicBond This is a

CONDENSATION reaction, where a water molecule is lost.

Glucose

Maltose

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sPolysaccharides

Polysaccharides are large complex molecules known as

POLYMERS.

Monomers are the individual monosaccharides which join to form the polysaccharide.

Polymerisation is the process of bonding many MONOMERS by condensation reactions to form one large molecule.

Return to isomerism of glucoseReturn to isomerism of glucoseNextNext

What is polymerisation

?

What is a monomer?

Click the bubble for the answer

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OOHOH

Forming polysaccharides

C C

C

C O

C

H

OH

OH

HH

CH2OH

H

H

C C

C

C O

C

H

OH

OH

OH

HH

CH2OH

H

H

O

H H

In this example, 3 condensation reactions have produced 3 water molecules to produce the polysaccharide.

O

H H

C C

C

C O

C

H

OH

OH

OH

HH

CH2OH

H

H

C C

C

C O

C

H

OH

OH

HH

CH2OH

H

H

OHOH OHOH

Glucose

O

O

H H

O

A HYDROLYSIS reaction (addition of water) reverses the reaction and splits the polysaccharide releasing 3 monosaccharide molecules.

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Polysaccharides• Polymers with subunits of monosaccharides• Repeated condensation reactions• Normally 1000’s of monomers • Polysaccharides are not sugars• Polysaccharides are insoluble• They are used for storage or construction

STARCH CELLULOSE GLYCOGEN

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sStarch

• Made up of two types of polysaccharide;

1) Amylose 2) Amylopectin

Amylose• Condensation reactions

between alpha glucose (1-4 glycosidic links).

• Forms a coiled helix

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sStarch

Amylopectin• Condensation reactions

between alpha glucose (1-4 glycosidic links).

• Branches of 1-6 glycosidic links also exist.

• Coiled springs with a

branched structure are formed.

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sStarch grains are a mixture of amylose & amylopectin

Starch is a polysaccharide

Starch it is a insoluble store of glucose

Starch is only found in plant cells, the animal equivalent is called GLYCOGEN.

It is ideal as a storage molecule because:• It is compact• Insoluble • Has no osmotic effect• Is readily broken down to mono and disaccharides

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sGLYCOGEN is the storage polysaccharide in animals

It has 1-4 glycosidic links

and 1-6 glycosidic linksIt is similar to amylopectin but has a greater number of shorter side branches

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sCellulose

• C1-4 links make up this polysaccharide.

• If C1 and C4 are to react, one glucose molecule needs to flip through 180o.

• It is this subtle difference that make cellulose so strong!

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Cellulose

Long straight chains of polysaccharideslinked together by hydrogen bonds

It is the hydrogen bonding between the straight chains that helps to give cellulose it’s strength.

Hydrogen bonds are formed between the hydroxyl groups of adjacent parallel chains

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s 70 chains of β glucose combine to form a MICROFIBRIL.

Lots of MICROFIBRILS are held together to form FIBRILS.

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Chitin• Forms the exoskeletons of insects-

lightweight and waterproof• Similar to cellulose but also has amino

acids to form a mucopolysaccharide• The OH groups are replaced by amino

acids

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sYou can give this question a go, in order to prove your understanding: